Manuel Juan-Espinosa

Negligible sex differences in general intelligence

Abstract The general factor, g , can be extracted from a correlation matrix of a battery of mental ability tests. g is common to all mental abilities. A key question in the research on cognitive sex differences is whether, on average, females and males differ in g . This question is technically the most difficult to answer and has been the least investigated. Cognitive batteries were applied in the present study to independent samples totaling 10,475 adult subjects (4,256 females and 6,219 males). The scores were factor-analyzed by sex to obtain separate g factors. The congruence coefficients ( r c ) suggested a near identity of these factors. Then, three methods were used to know if the standardized sex differences ( ds ) are explained by g : (1) the method of correlated vectors; (2) the sex loading in g was computed including the point-biserial correlation between sex and each of the subtests in the full matrix of subtest intercorrelations for factor analysis; and (3) the correlation between sex and g factor scores. The results suggest a negligible sex difference in g . The present study includes the largest sample on which a sex difference in g has ever been tested. The findings are consistent with those using quite different test batteries and subject samples.

Age dedifferentiation hypothesis: Evidence from the WAIS III

There is a renewed interest in the so-called age differentiation hypothesis—and the related age dedifferentiation hypothesis. The former states a reduction in the size of g at the first stage of life until early maturity. The latter hypothesized an increase in the importance of g at late adulthood and a decrease in the number of factors. The Spanish standardization of the WAIS-III (N=1369) was used in the present study to test the age dedifferentiation hypothesis. The results show no changes in the percentage of variance accounted for by g and four group factors (Verbal, Perceptual Organization, Working Memory, and Processing Speed) when the restriction of range is controlled. The ageindifferentiation hypothesis, as well as the anatomical metaphor, is proposed as a more fine-grained perspective to look at the development of the structure of cognitive abilities along the life span. D 2002 Elsevier Science Inc. All rights reserved.

Intelligence differentiation in adult samples

There is a renewed interest in the so-called differentiation theory. This theory states: the higher the level of g, the less the amount of g variance in any particular cognitive test. The implication of the differentiation theory for the scientific concept of intelligence is noteworthy: g could be more germane for low-ability than for high-ability people. A first battery of cognitive tests was applied to a sample of 3430 participants (mean age=23.12 years). The sample of the Spanish standardization of the WAIS-III was also analyzed (823 participants with a mean age=34.41 years). The methodology of Deary et al. [Intelligence 23 (1996) 105] was used for generating fine-grained low- and high-ability groups. The percentage of variance explained by g was computed for low- and high-ability groups, respectively: the mean percentages were 45.85 and 43.96 in the first cognitive battery, and 49.03 and 36.67 in the WAIS-III. These results support the differentiation of intelligence across the range of ability. However, a sample effect is observed: WAIS-III results are more supportive of the differentiation theory. This evidence suggests that ability differentiation could be related to educational differences. D 2003 Elsevier Science Inc. All rights reserved.

Education, Wechsler's Full Scale IQ, and g

The scientific construct of general intelligence (g) rests on the correlations among test scores, while IQ rests on the summation of standardized scores. Although IQ is usually considered a fine-grained proxy measure of general intelligence, IQ is actually an arbitrary variable (intelligence in general) not a scientific construct (general intelligence). This study examines the question of whether or not average Full Scale IQ (FSIQ) differences between groups that differ in their academic level can be attributed to g, because IQ results from g plus a mixture of specific cognitive abilities and skills. The Spanish standardization sample of the Wechsler Adult Intelligence Scale (WAIS-III) is analyzed. The sample comprised 703 females and 666 men aged 15–94 drawn as representative of the population in forms of educational level and geographical location. The results support the conclusion that the Wechsler FSIQ does not directly or exclusively measure g across the full range of the population distribution of intelligence. There is no significant association between the scientific construct of general intelligence (g) and the differences in intelligence in general (IQ) assessed by the WAIS-III. Some theoretical conclusions are stated as consequence of this lack of association. D 2002 Elsevier Science Inc. All rights reserved.

Sex differences in general intelligence defined as g among young adolescents

The g factor is common to all cognitive abilities and to measures of academic performance. An important question in the research on cognitive sex diAerences is whether, on average, females and males diAer in g. This question is technically the most diAcult to answer. Furthermore, it has been the least investigated. In the present study, two samples of young adolescents solved several cognitive and scholastic (achievement) tests. The samples were a total of 1565 young adolescents (797 girls and 768 boys). Sex was considered to obtain separate g factors. The congruence coeAcients between the g vectors extracted for each sex suggested a near identity. Then the sex diAerence in g was represented on each of the subtests in terms of a point-biserial correlation. These correlations were included with the full matrix of subtest intercorrelations for factor analysis. The results reveal the factor loading of sex on g, which in the present study suggest a null sex diAerence. # 2000 Elsevier Science Ltd. All rights reserved.

Generational IQ gains: Spanish data

Abstract There are thought-provoking data concerning massive IQ gains in the last fifty years. Flynn showed these gains in 14 nations. He suggests that these gains are symptomatic of the inadequacy of identifying IQ and intelligence, and that the gains are related to the ability to solve the type of abstract problems included in IQ tests (APSA, Abstract Problem Solving Ability). However, as Lynn (1990) has stated it is difficult to keep apart intelligence and abstract thinking. The gains are specially high in the domain of fluid abilities (Gf) and much less in crystallized abilities (Gc). These data support the possible nutritional effects over Gf, in the same way that dietary improvement has influenced height gains in the last 50 years. But there are other explanations as well. The present study analyzed data from the Spanish population (with time intervals between 28 and 16 years), not included in other datasets, and questions the APSA interpretation of the IQ gains.

Testing the age related differentiation hypothesis through the Wechsler's scales.

Abstract According to the age differentiation hypothesis (ADH), g becomes increasingly invested in specific abilities with age: with increasing age, g should account for a decreasing proportion of the variance in any particular cognitive test. However, there is no conclusive evidence concerning this important topic. Data from the Italian, Spanish, and American standardisation samples of the WPPSI and the WISC-R were analysed in the present study for testing the ADH. No changes in the proportion of variance associated with g in the 4–16 age range were found. This pattern does not change depending on the country. Therefore, the ADH is rejected: g seems to be very stable across age, and, thus, it seems to be an equally important component of intelligence test performance from early childhood to late adolescence.

Are cognitive sex differences disappearing? Evidence from Spanish populations

Sex differences in cognitive abilities were determined using the norms from two standardizations of the Differential Aptitude Test (DAT) and the Primary Mental Abilities (PMA) conducted between 1979 and 1995 in Spain. The standardized sex differences (ds) were computed separately for the DAT and the PMA subscales. Males scored higher in the DAT subscales Verbal Reasoning, Numerical Ability, Spatial Relations and Mechanical Reasoning, as well as in the PMA subscales Numerical Ability and Mental Rotation. Females scored higher in Inductive Reasoning (PMA-R) in the 1979 and 1995 standardizations. Taken together, these data do not support the hypothesis that cognitive sex differences are disappearing: there are still some differences favoring females and still some differences favoring males.

Individual differences in large-spaces orientation: g and beyond?

Abstract The relationships between the major abilities ( g , Gv and Gc) and general processes in wayfinding (Updating one’s position, Route representation, and Survey representation) are analyzed. Seven wayfinding tasks were developed for the present study: two of them were field tasks and five were computerized. The participants were 111 psychology undergraduate students. Updating tasks were used as a criterion measure of large-scale space orientation. We tried to isolate the g effects over Gc and Gv. Structural equation modeling was used for the analyses. Results indicated that Updating one’s position was influenced by g and Gv_ s (Gv_specific part), but not by Gc_ s (Gc_specific part) or the remaining orientation processes. However, some of the Updating variance remains unexplained.

Does g variance change in adulthood? Testing the age de-differentiation hypothesis across sex

In the last decade, changes in the structure of intelligence across the life-span has become a central topic in the research on human intelligence. One of the main hypotheses that has arisen to account for such changes has been the age de-differentiation hypothesis [Balinsky, Genetic Psychology Monographs 23 1941, 191]. It predicts an increase in the importance of g, and a decrease in the number and importance of the lower-order abilities from early maturity to senescence. Despite of the research effort to test this hypothesis, no study has ever been conducted controlling by sex. For that purpose, males and females of the Spanish standardisation sample of the WAIS-III were analysed separately. Results show that the importance of g does not change with age irrespective of sex. Thus, the age de-differentiation hypothesis is rejected for both males and females. The indifferentiation hypothesis is supported as a more appropriate view of the changes in the structure of intelligence across adulthood.